Types of Bonding
Physically hardening adhesives 2 2
Drying Adhesives They are made of polymers dissolved in solvent (Polychloroprene, Polyurethane) or dispersed in water (white glue based on PVA (Polyvinyl acetate, cellulose, casein, polyvinyl alcohol or polyvinyl pyrrolidone composition). The setting process of bonding is obtained by solvent evaporation, water evaporation or coalescence (When water or solvant is evaporated, the polymers molecules become closer and closer until to form a continous film adhesive) of a waterbased dispersion polymer. Depending on the chemical composition of the adhesive, they will adhere to different materials to greater or lesser degrees. These adhesives are typically used for cellulosic supports (paper, cardboard and wood) or household applications. 3
Contact Adhesives They are made of Natural Rubber and polychloroprene (Neoprene). They must be applied to both surfaces and allowed some time to dry before the two surfaces are pressed together. Once the surfaces are pushed together, the bond forms very quickly, hence, it is usually not necessary to apply pressure for a long time. So there is no need to use clamps. Contact adhesives find use in furniture and footwear Industries. 4
Hot Melt Adhesives These solventless adhesives are based on thermoplastic materials. A thermoplastic is a polymer that turns to liquid when heated and freezes to a solid upon cooling The hot-melt adhesive is heated and applied in its liquid state with the aid of glue guns or nozzles and the bonding is obtained in few seconds by cooling. Hot melt adhesives are used in packaging, book binding, textiles, footwear and furniture, automotive, electronic industries. 5
Pressure Sensitive Adhesives (PSA) Pressure Sensitive is a term commonly used to designate a distinct category of adhesives based on elastomeric materials, such as Styrene Block Copolymers, which in dry form are permanently tacky at room or low temperature. This adhesive forms a bond when pressure is applied to marry the adhesive with the substrate. Pressure sensitive adhesives are designed for both permanent or removable applications and some high performance permanent PSA exhibit high adhesion values. They are used in pressure sensitive tapes, labels, note pads, automobile trim, and a wide variety of other products. 6
Summarisation Description Bonding mechanism Base raw materials Area of application Hotmelts Solidification Ethylene/ vinyl acetate copolymers, polyamides, polyesters, etc. Packaging, printing, textiles, shoe-making and woodworking, car manufacturing, electrical engineering. Wet Solvent containing adhesives Evaporation of solvent Polymeric vinyl coumpounds, polymethyl methalcrylate, natural and synthetic rubber, etc. Printing and packaging, bonding PVC pipes, adhesives used in the home Contact adhesives Evaporation of solvent Polychloroprene, butadieneacrylonitrile, rubber, etc. Floor coverings, mattress and shoe manufacturing, car manufacturing Dispersion adhesives Evaporation of water Non water-soluble copolymers of vinyl acetate, also in combination with co-monomer, polyacrylates, etc Packaging, shoe-making, woodworking Other water-based adhesives Evaporation of water Glutin, casein, dextrin, cellulose, polyvinyl alcohol, etc. Paper, wallpaper Pressure sensitive adhesives Via surface contact of tacky layers Special polyacrylates, polyvinyl ether, natural rubber, etc. Adhesives tapes for handicraft work and industrial use, plasters, sticky labels Plastisols Sol-gel process on heating PVC and plasticisers Vehicle bodywork construction 7
Chemically hardening adhesives 8 8
Polyurethane Adhesives Polyurethanes adhesives are based on Polyisocyanates and Polyether / Polyester Polyols chemistry. They are available in one or two components systems. The one component adhesive (PU1K) reacts with air humidity and can be applied at room temperature (PUR) or at high temperature like a hot-melt adhesive (HMPUR). The two components adhesive (PU2K) needs to be mixed according specific ratio before use. They find use in Industrial Assembly, flexible packaging, windsceen bonding. 9
Epoxy Resin Adhesives Epoxy adesives are a major part of the class of adhesives called structural adhesives". As for the polyurethanes, they can be one or two components systems. The one component epoxy needs to be cured at high temperature, whereas the two components epoxy bond at room temperature. They can be made flexible or rigid, transparent or opaque/colored, fast setting or extremely slow setting. These high-performance adhesives are used in many applications (transportation, golf clubs, skis, snow boards, household) where high strength bonds are required. 10
Anaerobic Adhesives anaerobic adhesives based on diacrylate chemistry are single-component adhesives that harden rapidly to form a strong bond between surfaces from which air is excluded. Oxygen is an inhibitor for anaerobic adhesives. In the presence of oxygen in air, the product does not react and stays liquid. These two following conditions are needed for proper cure: Contact with a metal surface. Absence of oxygen or air. They are recommended for use on metal surfaces, for threadlocking of nuts and bolts 11
Cyanoacrylate Adhesives Cyanoacrylate adhesives are one-part acrylate adhesives often called Super glues. Cyanoacrylate adhesives cure instantly on contact with mated surfaces through a reaction with surface moisture (anionic polymerisation). They are used in Industrial and consumer glues, in the veterinary glues and in medical applications. 12
Silylated Polymer Adhesives Moisture curable Silylated Adhesives & Sealants are a part of these last years recent developments. Silane-modified adhesives and sealants based on SMP (Silane modified polymer) are designed as onecomponent systems. SMP adhesives have to be applied from 5 C to 30 C and bond within 10-30 minutes by reaction with air humidity. Due to their chemical structure these kind of polymers exhibit good weathering and aging resistance as well as an almost universal adhesion spectrum without need of primers. They excel where elastic construction joints are required 13
Silicone Adhesives Silicone adhesives are based on Polysiloxanes chemistry which allows high flexibility even at low temperature as well as humidity and temperature resistance. They are available in one or two components systems. Both systems cure by polycondensation initiated by moisture for the one component system and by reaction of a silicic acid ester with polysiloxane for the two components system. Silicone adhesives give moisture resistant bonds for glass and ceramics therefore is mainly used for sealing joint in sanitary application. 14
Summarisation Description Curing mechanism Base raw materials Areas of application Cyanoacrylates Polymerisation Cyanoacrylates Bonding small components, bonding all types of glass, fabric adhesives, spray-on bandages Methyl methacrylates Polymerisation Methyl methacrylates Bonding plastics in the car and rail vehicle manufacturing industries Anaerobically curing adhesives Polymerisation Rol diacrylates Engines, electric motors, securing screws, cam-shaft connections Phenol-formaldehyde resins Polymerisation Phenols, formaldehyde Wood materials, bonding brake and clutch linings, structural bonding of aluminium in aircraft manufacture Silicones Polycondensation Polyorganosiloxanes Seals, car manufacturing, electrical enginnering; special applications in aeronautics and aerospace technology Polyimides Polycondensation Aromatic tetracarboxylic anhydrides and aromatic diamines Bonding metals in aeronautics and aerospace technology Epoxy resin adhesives Polycondensation Oligomeric diepoxides and polyamines or polyamidoamines Structural adhesives in car and aircraft manufacture; vehicle bodywork construction, electronics, bonding fibre-reinforced plastics, repair work Polyurethanes Polyaddition Di-functional and sometimes trifunctional isocyanates, polyols, polyether, polyesther Vehicle bodywork construction, bonding materials with very different load and temperature expansion properties, bonding panes of glass in car manufacture 15